Hundreds of people descended on California minutes after it was announced that Donald Trump had won the election.
Hillary Clinton supporters were filmed setting fire to the US flag while marching through the streets of Portland, Oregon, shouting "F*** Donald Trump".
Footage also emerged of activists setting tyres and rubbish bins on fire, blocking main roads and lighting flares.
People also burned an effigy of the President-elect, who will be officially sworn into office in January.
Other protests have broken out in the San Diego, San Fransisco and San Jose areas, according to reports by Mirror.
People could be heard chanting "Whose streets? Our streets" and "Not Our President", according to Twitter users at the scene.
A demonstration also unfolded at the University of California, Davis where students blocked streets as they marched and chanted anti-Trump slogans and "You are not America, we are America," according to Twitter posts.
Anti-racist protesters are to stage a demonstration outside the US Embassy in London following the shock election victory. more photos after the cut: